Coupler to Launch Electromagnetic Signal from Microstrip to Dielectric Waveguide

ABSTRACT

A metallic waveguide is mounted on a multilayer substrate. The metallic waveguide has an open end formed by a top, bottom and sides configured to receive a core member of a dielectric waveguide, and an opposite tapered end formed by declining the top of the metallic waveguide past the bottom of the metallic waveguide and down to contact the multilayer substrate. A pinnacle of the tapered end is coupled to the ground plane element, and the bottom side of the metallic waveguide is in contact with the multiplayer substrate and coupled to the microstrip line.

CLAIM OF PRIORITY UNDER 35 U.S.C. 119(e)

The present application claims priority to and incorporates by referenceU.S. Provisional Application No. 61/803,435 (attorney docket TI-73114PS)filed Mar. 19, 2013, entitled “Dielectric Waveguides.”

FIELD OF THE INVENTION

This invention generally relates to wave guides for high frequencysignals, and in particular to a coupling structure to launch anelectromagnetic signal from a microstrip into a dielectric waveguide.

BACKGROUND OF THE INVENTION

In electromagnetic and communications engineering, the term waveguidemay refer to any linear structure that conveys electromagnetic wavesbetween its endpoints. The original and most common meaning is a hollowmetal pipe used to carry radio waves. This type of waveguide is used asa transmission line for such purposes as connecting microwavetransmitters and receivers to their antennas, in equipment such asmicrowave ovens, radar sets, satellite communications, and microwaveradio links.

A dielectric waveguide employs a solid dielectric core rather than ahollow pipe. A dielectric is an electrical insulator that can bepolarized by an applied electric field. When a dielectric is placed inan electric field, electric charges do not flow through the material asthey do in a conductor, but only slightly shift from their averageequilibrium positions causing dielectric polarization. Because ofdielectric polarization, positive charges are displaced toward the fieldand negative charges shift in the opposite direction. This creates aninternal electric field which reduces the overall field within thedielectric itself. If a dielectric is composed of weakly bondedmolecules, those molecules not only become polarized, but also reorientso that their symmetry axis aligns to the field. While the term“insulator” implies low electrical conduction, “dielectric” is typicallyused to describe materials with a high polarizability; which isexpressed by a number called the dielectric constant (ck). The terminsulator is generally used to indicate electrical obstruction while theterm dielectric is used to indicate the energy storing capacity of thematerial by means of polarization.

The electromagnetic waves in a metal-pipe waveguide may be imagined astravelling down the guide in a zig-zag path, being repeatedly reflectedbetween opposite walls of the guide. For the particular case of arectangular waveguide, it is possible to base an exact analysis on thisview. Propagation in a dielectric waveguide may be viewed in the sameway, with the waves confined to the dielectric by total internalreflection at its surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Particular embodiments in accordance with the invention will now bedescribed, by way of example only, and with reference to theaccompanying drawings:

FIG. 1 is a plot of wavelength versus frequency through materials ofvarious dielectric constants;

FIGS. 2A-2D illustrate various configurations of dielectric waveguides(DWG) produced using printed circuit board technology;

FIGS. 3A-3C together are an orthographic projection of an exampledielectric waveguide;

FIG. 4 is a flow chart illustrating a process for fabricating adielectric waveguide.

FIG. 5 is an isometric view of a reflector for use with a dipoleantenna;

FIG. 6 is a sectional view of the reflector of FIG. 6;

FIG. 7 is a plot showing insertion loss for the dipole antenna andreflector of FIG. 5;

FIGS. 8A and 8B illustrate another embodiment of a DWG coupled to anintegrated circuit (IC);

FIGS. 9-10 illustrate embodiments for interfacing a DWG directly to anIC;

FIGS. 11-13 illustrate simulations of radiated energy from various DWGinterface configurations;

FIG. 14 is a plot illustrating insertion loss for various interfaceconfigurations;

FIG. 15 illustrates two DWGs coupled with a snap connecter with asilicon gap filler material;

FIGS. 16A-16B illustrate simulations of radiated energy from a rightangle corner of a DWG;

FIG. 17 is an illustration of a DWG that has a right angle corner thatis shielded to minimize radiation leakage;

FIGS. 18A-18B illustrate a simulation of radiated energy from a shieldedright angle corner of a DWG;

FIG. 19 is a plot illustrating insertion loss vs. frequency for a DWGwith a right angle bend;

FIG. 20 is an illustration of an example flexible DWG;

FIGS. 21A-21D illustrate various configurations of a multichannelflexible DWG;

FIGS. 22-25 illustrate various ways of combing a flexible DWG with aflexible cable;

FIG. 26 illustrates a microelectronic package with a dipole antennacoupled to a DWG that has director elements to improve coupling of aradiated signal;

FIGS. 27A-27C are multiple views of a structure for launching a signalfrom a stripline to a DWG;

FIG. 28 illustrates simulation results for various length metallicwaveguide transitions;

FIG. 29 is an isographic view of a horn antenna used to launch a signalfrom a microstrip line to a DWG;

FIGS. 30A and 30B are top and front views of the horn antenna of FIG.29;

FIG. 31 illustrates a simulation of signal radiation from the hornantenna of FIG. 29;

FIG. 32 illustrates use of an RJ45 connector for coupling a DWG;

FIGS. 33-34 illustrates various applications of an RJ45 connector forcoupling a DWG;

FIG. 35 is a flow chart illustrating use of a DWG in a system; and

FIG. 36 is an illustration of two systems being interconnected with aDWG.

Other features of the present embodiments will be apparent from theaccompanying drawings and from the detailed description that follows.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency. In thefollowing detailed description of embodiments of the invention, numerousspecific details are set forth in order to provide a more thoroughunderstanding of the invention. However, it will be apparent to one ofordinary skill in the art that the invention may be practiced withoutthese specific details. In other instances, well-known features have notbeen described in detail to avoid unnecessarily complicating thedescription.

As frequencies in electronic components and systems increase, thewavelength decreases in a corresponding manner. For example, manycomputer processors now operate in the gigahertz realm. As operatingfrequencies increase sub-terahertz, the wavelengths become short enoughthat signal lines that exceed a short distance may act as an antenna andsignal radiation may occur. FIG. 1 is a plot of wavelength versusfrequency through materials of various dielectric constants. Asillustrated by plot 102 which represents a material with a lowdielectric constant of 3, such as a printed circuit board, a 100 GHzsignal will have a wavelength of approximately 1.7 mm. Thus, a signalline that is only 1.7 mm in length may act as a full wave antenna andradiate a significant percentage of the signal energy.

Waves in open space propagate in all directions, as spherical waves. Inthis way they lose their power proportionally to the square of thedistance; that is, at a distance R from the source, the power is thesource power divided by R2. A wave guide may be used to transport highfrequency signals over relatively long distances. The waveguide confinesthe wave to propagation in one dimension, so that under ideal conditionsthe wave loses no power while propagating. Electromagnetic wavepropagation along the axis of the waveguide is described by the waveequation, which is derived from Maxwell's equations, and where thewavelength depends upon the structure of the waveguide, and the materialwithin it (air, plastic, vacuum, etc.), as well as on the frequency ofthe wave. Commonly-used waveguides are only of a few categories. Themost common kind of waveguide is one that has a rectangularcross-section, one that is usually not square. It is common for the longside of this cross-section to be twice as long as its short side. Theseare useful for carrying electromagnetic waves that are horizontally orvertically polarized.

For the exceedingly small wavelengths encountered for sub-THz radiofrequency (RF) signals, dielectric waveguides perform well and are muchless expensive to fabricate than hollow metal waveguides. Furthermore, ametallic waveguide has a frequency cutoff determined by the size of thewaveguide. Below the cutoff frequency there is no propagation of theelectromagnetic field. Dielectric waveguides have a wider range ofoperation without a fixed cutoff point. Various types of dielectricwaveguides and techniques for coupling a dielectric waveguide to anintegrated circuit or to another dielectric waveguide are describedherein.

FIGS. 2A-2D illustrate various configurations of dielectric waveguidesproduced using printed circuit board technology. A dielectric waveguidemay be used as an interconnect for chip to chip high data ratecommunication on a printed circuit board (PCB). Embodiments of thisdielectric waveguide are capable of being assembled in a manufacturingline as an additional surface mount part and are able to resist alead-free solder reflow process during assembly of the PCB.

FIG. 2A illustrates a multilayer PCB 200 that contains severalconductive layers separated by insulating layers. The various conductivelayers may be patterned into interconnect patterns and interconnected byvias, as is well known Vias are also brought to the surface of the PCBand provide connection pads for an integrated circuit (IC) substrate210. Solder balls 202 provide an electrical connection between the pinson carrier 210 and the via pads on PCB 200, as is well known. IC 240 ismounted on substrate 210 and contains circuitry that generates a highfrequency signal using known techniques.

IC 210 includes high frequency circuitry that produces a signal that isconnected to dipole antenna 212. A dielectric waveguide 220 isinterfaced to the dipole antenna and reflector 214 by an interfaceregion 222 that may be part of the dielectric waveguide. Dielectricwaveguide (DWG) 220 is mounted on PCB 200 and must be able to withstandthe reflow process that is used to attach IC 210 to the PCB.

Dielectric waveguide 220 may be fabricated using standard PCBmanufacturing techniques. PCB manufacturers have the ability to createboard materials with different dielectric constants by usingmicro-fillers as dopants, for example. A dielectric waveguide may befabricated by routing a channel in a low dielectric constant (∈k2) boardmaterial and filling the channel with high dielectric constant (∈k1)material. FIGS. 2B-2D illustrate three interface options that may beused to interface DWG 220 with microelectronic device substrate 210.FIG. 2B illustrates an interface region 222 that is formed by a metallicwaveguide that it is made using vertical walls of copper and top andbottom copper layers (not shown in the drawing). DWG core member 225 ismade from a material having a high dielectric constant, while cladding226 is made from PCB material that has a lower dielectric constant. FIG.2C illustrates a similar idea but a horn 223 is formed to help capturemore radiation from the dipole antenna of the microelectronic devicesubstrate 210. FIG. 2D illustrates an approach that does not use ametallic waveguide. The interface is simply made between the dipoleantenna 212 of IC carrier substrate 210 and dielectric mating edge 224of waveguide 220. Any one of these three waveguide designs may bemanufactured by repeating it many times in a PCB and then sawing the PCBboard into individual waveguides that can be used as individual surfacemount parts.

FIGS. 3A-3C together are an orthographic projection of an exampledielectric waveguide 300 that is similar to FIG. 2B that is fabricatedusing a typical PCB manufacturing technique. FIGS. 3A-3C illustrate howDWG 300 is fabricated. In this example, three DWGs 300-302 areillustrated as being sliced from a single PCB; however, this is forillustration only and typically a larger number of DWGs may befabricated on one PCB and then sliced into individual DWGs along cuttinglines 320. Note that DWG 302 includes two channels; a larger number ofchannels may be fabricated in the same manner.

FIG. 4 is a flow chart illustrating a process for fabricating adielectric waveguide. Referring also to FIG. 3, a PCB initial substratelayer 310 includes a copper, or other conductive layer 311 that isetched to form a bottom side for metallic waveguide portion 222, or 223,referring again to FIG. 2B, 2C. Copper layer 311 is omitted when a DWGas illustrated in FIG. 2D is fabricated. A grove is formed 402 intosubstrate layer 310 for each DWG channel. The channel is typicallyrectangular, typically twice as wide as it is deep. The dimensions areselected based on the frequency and resulting wavelength that the DWG isintended to transport, based on known waveguide theory. The channels maybe formed by various known techniques, such as: mechanical routing ormilling, by scraping with a chisel bit, by etching through a mask usingchemical etchant or media blasting, etc.

Sidewalls 315, 316 for a metallic waveguide portion, such as portion222, or 223, referring again to FIG. 2B, 2C, may be formed using aprocess similar to forming vias. Similar to forming holes for a via, atrench is routed for each sidewall and then plated with a processsimilar to that used for vias. The dimensions of the metallic waveguideportion may be similar to the dimensions for the dielectric coreportion, or one may be somewhat larger than the other. The process offorming the channel groves may also remove the material between thesidewalls after the sidewalls have been formed.

Once the channels are formed, they may be filled 404 with a PCB boardmaterial that has a higher different dielectric constant to form coremembers 318. PCB substrate layer 310 typically has a dielectric constantvalue that may be in the range of approximately 2.5-4.5. Micro-fillersmay be used as dopants to raise the dielectric constant value of coremember 318 so that core member 318 has a higher dielectric constant thancladding material 310, 312, and 314. Typically, the dielectric constantof the core member may be selected from a range of values ofapproximately 3-12 using commonly available materials and dopants.Various types of material may be used as a dopant, such as: ZnO, orBaTiO3, for example. PCB and filler materials are available from varioussources, such as Roger Corporation: RO3003 for the PCB, and RO3006 orRO3010 for the filler, for example.

A top layer 314 that also has an etched copper layer 313 may belaminated 406 on top of substrate layer 310 to form a top portion ofcladding 226. In some embodiments, the top layer 314 may be omitted andthe sliced DWG may be mounted upside down on a PCB carrier board, suchas PCB 200, to form the remaining cladding portion. In otherembodiments, the top layer may be omitted and air, which has adielectric constant of approximately 1.0, will form the top portion ofthe cladding. Optionally, a conformal coating or other protective layermay be applied over planar layer 310 in embodiments in which top layer314 is omitted. Typically, when the DWG will not be subjected totouching by human or other nearby objects, the top layer may be omittedto save expenses.

Planar layer 310 is then sliced 408 to produce the individual DWG300-302, for example. Each individual DWG may contain one channel, or itmay contain two or more channels, depending on how planar layer 310 issliced.

The individual DWG may then be mounted 410 on a carrier PCB and used totransport sub-terahertz signals that are produced by an integratedcircuit, such as IC 240.

Referring again to FIG. 2A, dipole antenna 212 and reflector 214 providea structure to launch a signal from a microelectronic device into adielectric waveguide. On the other end of the dielectric waveguideinterconnect, a similar structure may be used to acquire the signal fromthe waveguide into the microelectronic device.

Dipole antenna 212 may be used by the microelectronic device to radiatethe signal into a dielectric waveguide 220 that is located outside thepackage but very close to it. By its nature, dipole antenna 212 willradiate in a very oriented radiation pattern towards the dielectricwaveguide but also in the direction opposite to it, which is towards thecore of the package. A reflector on the backside of the dipole antennawill reflect the radiation radiated towards the center of the packageback in the direction of the dielectric waveguide.

Two different launching structure designs will now be described in moredetail. One design is useful for interfacing with a dielectric waveguidein a direction coplanar with the PCB, while the second design is usefulfor interfacing with a dielectric waveguide placed perpendicular to theplane defined by the PCB.

FIG. 5 is an isometric view and FIG. 6 is a sectional view of areflector array 514 for use with a dipole antenna 512, which is anexpanded view of the dipole antenna 212 and reflector 214 illustrated inFIG. 2A. Referring back to FIG. 2A, note the location of dipole antenna212 and reflector 214 within substrate 210. An outside edge of carrier212 forms an interface surface 211 that is configured for interfacing toDWG 220. Reflector structure 214 is formed in the carrier substrateadjacent to dipole antenna 212 and opposite from the interface surface211.

Referring again to FIG. 5, differential signal lines 513 connect thedipole antenna 512 to IC 240 that is generating or receiving asub-terahertz high frequency signal.

Ground plane 505 orients a signal launched from dipole antenna 512 in adirection towards DWG 520, but also in a direction away from DWG 520.Reflector 514 is an array of metalized vias between two coplanar plates515, 516 that are above and below the plane that holds the dipoleantenna 512. In some embodiments, there may be an additional reflectorstrap 517 coupled to the array of vias and running essentially parallelto the dipole antenna in the same plane as the dipole antenna.Additional parallel reflector straps may be added on other layers, ifpresent. The goal is to erect an essentially vertical metallic “wall”that reflects radiated energy from dipole antenna 512 back towards DWG520. The vias may be connected to ground, or may be left floating. Themetal structure acts a “short” to the radiated field from the dipoleantenna. Spacing the metal reflector structure approximately one half ofa wavelength from the dipole antenna provides an optimum amount ofreflection. Alternatively, the reflector structure may be placed adistance of 1.5, 2.5, etc wavelengths from the dipole antenna. While adistance of one half wavelength is optimum, a distance in the range of0.3-0.7 or multiples thereof provides a useful amount of reflection.

FIG. 7 is a plot showing insertion loss for dipole antenna 512 andreflector 514 based on a simulation of this configuration. Note theinsertion loss is fairly constant at approximately −2.6 db up to about168 GHz.

FIGS. 8A and 8B illustrate another embodiment of a DWG coupled 820 to anintegrated circuit 240. In this embodiment, DWG 820 is interfaced to aninterface surface 811 on the bottom side of carrier 810 that isconfigured for interfacing DWG 820 through a hole in PWB 800. Areflector structure 818 is formed in the carrier substrate adjacent todipole antenna 812 and opposite from the interface surface 811. In thisembodiment, reflector structure 818 may be a metallic plate positionedabove dipole antenna 812. Spacing the metal reflector structureapproximately one half of a wavelength from the dipole antenna providesan optimum amount of reflection. Alternatively, the reflector structuremay be placed a distance of 1.5, 2.5, etc wavelengths from the dipoleantenna. While a distance of one half wavelength is optimum, a distancein the range of 0.3-0.7 or multiples thereof provides a useful amount ofreflection. Reflector plate 818 may be connected to ground, or may beleft floating.

FIG. 8B is a plot illustrating insertion loss for dipole antenna 812 andreflector 814 based on a simulation of this configuration. Note theinsertion loss is less than approximately −2 db up to about 166 GHz.

As can be seen, a reflector structure in combination with a dipoleantenna provides a good way to launch or receive sub-terahertz signalsthat are generated or received by an integrated circuit. The twoembodiments described herein provide a low insertion loss and are easyto implement. They provide implementation options for applications thatneed parallel or perpendicular orientation of the dielectric waveguideswith respect to the PCB.

FIGS. 9-10 illustrate embodiments for interfacing a DWG directly to anIC. A chip scale package (CSP) is a type of integrated circuit chipcarrier. In order to qualify as chip scale, the package typically has anarea no greater than 1.2 times that of the die and it is a single-die,direct surface mountable package. Another criterion that is oftenapplied to qualify these packages as CSPs is their ball pitch should beno more than 1 mm. The die may be mounted on an interposer upon whichpads or balls are formed, like with flip chip ball grid array (BGA)packaging, or the pads may be etched or printed directly onto thesilicon wafer, resulting in a package very close to the size of thesilicon die. Such a package is called a wafer-level chip-scale package(WL-CSP) or a wafer-level package (WLP).

A technique for interfacing a microelectronic device directly with adielectric waveguide used for THz RF communication will now bedescribed. At frequencies above sub-THz, copper cannot be used toconduct an electromagnetic signal due to extreme increase in impedancedue to the known ‘skin depth effect’. As discussed above, anelectromagnetic RF signal may be transported using a dielectricwaveguide that may have dimensions similar to the DWG described abovefor signals at sub-THz frequency.

Referring to FIG. 9, in this example, a Chip Scale Package 940constitutes a microelectronic device. In CSP devices, semiconductorlogic and circuits that may produce or receive a sub-THz RF signal areformed in an epi-layer 943. In this example, CSP 940 is mounted on a PCB900 that may have additional devices mounted to it. In this example,solder bumps 941 secure SCP 940 to PCB 900; however, in otherembodiments different types of mounting schemes that are now known orlater developed may be used.

The RF signal may be conducted to the opposite side of the chip usingthrough-silicon-via (TSV) technology. A through-silicon via is avertical electrical connection (Vertical Interconnect Access) passingcompletely through a silicon wafer or die. TSVs are a high performancetechnique used to create 3D packages and 3D integrated circuits.Compared to alternatives such as package-on-package, TSVs provide adensity of the vias that may be substantially higher, and provideconnection lengths that may be shorter.

On the opposite side of the chip from epi layer 943, a patternedmetallization constitutes an antenna 944 to transmit and/or receive theRF signal from a dielectric waveguide 920. In this example, DWG 920 ismounted vertically, i.e., perpendicular to the chip. FIG. 10 illustratesand example where the DWG is mounted horizontally, i.e. parallel to thechip. The metalized antenna may be formed is several ways, such as byusing sputtering, thermal or e-gun evaporation technologies, forexample. This metallization may be realized using various known or laterdeveloped metallization process, such as forming a Titanium layer incontact with the Si to work as a adhesion layer, forming an Ni layer ontop of the Titanium to work as a barrier layer (to avoid contaminationof the Si die) and above this last layer forming a layer of Aluminum,Copper, Gold or any other metal with high electrical conductivity, forexample.

The antenna may be patterned in the back side of the silicon die using ahard mask or using a photolithography process, for example. The antennamay be a simple dipole antenna, a Marconi antenna, or a more elaboratepatch antenna, for example. In this example, two through silicon vias945, 946 provide a differential RF signal to/from the antenna to epilayer 943.

A ground plane 942 embedded in PCB 900 is used as an electromagneticreflector to reflect back towards the dielectric waveguide the signalthat the antenna may be sending in the direction opposite to thedielectric waveguide. Under-fill material 941 may be installed to attachDWG 920 to SCP 940.

This technique results in low insertion loss between SCP 940 and DWG920, is easy to implement, and uses standard manufacturing materials andfabrication techniques.

FIG. 10 illustrates an example system that includes a PCB 1000 uponwhich are mounted SCP 1040-1 and 1040-2. SCP 1040-1 includes circuitrythat generates a sub-terahertz or terahertz signal that is conveyed toSCP 1040-2 via DWG 1020 using through silicon vias to a back mountedantenna, as described above. Similarly, SCP 1040-2 includes circuitrythat receives the sub-terahertz or terahertz signal that is conveyed viaDWG 1020 using through silicon vias coupled to a back mounted antenna,as described above. PCB 1000 is similar to PCB 900 and includes a groundplane for reflecting energy radiated by a dipole antenna in SCP 1040-1back towards DSG 1020. In this example, DWG 1020 has an interfacesurface on its side at each end for interfacing with the antennas on theback side of SCP 1040-1 and 1040-2 which allows DWG 1020 to be mountedhorizontally from chip to chip.

In some embodiments, a short section of DWG may be permanently attachedto a CSP or other type of packaged IC, as illustrated above with respectto FIG. 2A, 8A, 9, or 10 to form a module. It may then become necessaryto couple the DWG segment included in the module to another DWG segment.Various schemes for interfacing segments of DWG will now be described.

FIGS. 11-13 illustrate simulations of radiated energy for various DWGinterface configurations. This interface could be used to connect twoidentical waveguides to extend the length, for example, or to connecttwo different waveguides in the case where one of them may be part of anelectronic device such as: a computer, server, smart-phone, tablet orany other communication device, etc. For example, a DWG segment that ispart of an IC module may be coupled to another DWG segment.

When two dielectric waveguides are coupled together, there is likely tobe a gap between the two DWGs. This gap creates an impedance mismatchthat may generate significant losses due to radiated energy produced bythe impedance mismatch. The extent of the losses depends on the geometryof the gap and the material in the gap. Based on simulations, a squarecut butt joint appears to provide a significant impedance mismatch.

FIG. 11 illustrates a simulation result for an inclined cut interfacebetween two DWG segments 1101, 1102. The core member is indicated at1125 and the cladding is indicated at 1126. In this example, gap 1104 isapproximately 1.2 mm. Note that there is a significant amount ofradiated energy, such as indicated by shaded regions 1106. In FIG. 14,plot line 1401 illustrates insertion loss vs. gap length for an inclinedcut interface.

FIG. 12 illustrates a simulation result for a spearhead shaped cutinterface between two DWG segments 1201, 1202. The core member isindicated at 1225 and the cladding is indicated at 1226. In thisexample, gap 1204 is approximately 1.2 mm. Note that there is a muchsmaller amount of radiated energy, such as indicated by shaded regions1206. In FIG. 14, plot line 1402 illustrates insertion loss vs. gaplength for a spear shaped interface.

This spearhead is effective if the taper is done in only two of thesides of the DWG but it is better when the taper is done in the foursides of the DWG to form a pyramidal shape. This taper could also bereplaced by a conical shape on four sides or a vaulted shape on twosides, or any other shape that deflects energy back to the DWG from thesignal deflected by the opposite side cut.

A spearhead, pyramidal, conical, vaulted or similar type shape providesan interface with a very low insertion loss, is easy to implement, ismechanically self-aligning, and is flexible and robust to smallmisalignments. These shapes may all be produced using standardmanufacturing materials and fabrication techniques.

A simulator known as “High Frequency Simulator Structure” (HFSS),(available from ANSYS, Inc) was used analyze the various shapesdiscussed above. HFSS is a high performance full wave electromagnetic(EM) field simulator for arbitrary 3D volumetric passive devicemodeling. It integrates simulation, visualization, solid modeling, andautomation using a finite element method (FEM) and an integral equationmethod. HFSS can extract scattering matrix parameters (S, Y, Zparameters), visualize 3-D electromagnetic fields (near and far-field),and generate Full-Wave SPICE models that link to circuit simulations.

Material in the Gap

In the examples discussed above, the material filling the gap is justair, which has a dielectric constant of approximately 1.0. As discussedearlier, the dielectric constant of the core material will typically bein the range of 3-12, while the dielectric constant of the claddingmaterial will typically be in the range of 2.5-4.5. The mismatchimpedance is proportional to the difference of the dielectric constantbetween the DWG and the material inside the gap. This means that evenwith the geometry of the socket optimized, an air gap between the DWGsis not an optimum configuration. In order to minimize the impedancemismatch, a DWG socket may be designed with a rubbery material that hasa dielectric constant very close to the dielectric constant of the DWGcore and cladding. A flexible material is desirable to accommodate andfill all the space in the gap. An example of a rubbery material withdielectric constant 2.5 to 3.5 is Silicone. Other materials with similarcharacteristics that may be used fall into two types: unsaturated rubberand saturated rubber.

Unsaturated rubbers include: Synthetic polyisoprene, Polybutadiene,Chloroprene rubber, Butyl rubber, Halogenated butyl rubbers,Styrene-butadiene Rubber, Nitrile rubber, Hydrogenated Nitrile Rubbers,etc, for example.

Saturated rubbers include: EPM (ethylene propylene rubber), EPDM rubber(ethylene propylene diene rubber), Epichlorohydrin rubber (ECO)Polyacrylic rubber (ACM, ABR), Silicone rubber (SI, Q, VMQ),Fluorosilicone Rubber (FVMQ, Fluoroelastomers (FKM, and FEPM) Viton,Tecnoflon, Fluorel, Perfluoroelastomers (FFKM) Tecnoflon PFR, Kalrez,Chemraz, Perlast, Polyether block amides (PEBA), Chlorosulfonatedpolyethylene (CSM), (Hypalon), Ethylene-vinyl acetate (EVA), etc, forexample.

FIG. 13 illustrates a simulation result for a spearhead shaped cutinterface between two DWG segments 1301, 1302. The core member isindicated at 1325 and the cladding is indicated at 1326. In thisexample, gap 1304 is approximately 1.2 mm and is filled with a siliconmaterial. Note that there is a negligible amount of radiated energy.

FIG. 14 is a plot illustrating insertion loss for various interfaceconfigurations versus gap length. Plot line 1403 illustrates insertionloss vs. gap length for a spear shaped cut interface with a siliconrubber gap filler. Plot line 1401 illustrates insertion loss vs. gaplength for an inclined cut interface. Plot line 1402 illustratesinsertion loss vs. gap length for a spear shaped cut interface.

It can be seen that using an optimized design with the spearheadgeometry and filling the gap with Silicone material results in under 1dB of attenuation for gaps as large as 1.5 mm, as illustrated by plotline 1403.

As the gap gets narrower, approaching 0.0 mm, the insertion loss for anyof the configurations reduces to approximately zero; however, typicallya gap of 0.0 is difficult to maintain when using economical,non-precision DWGs.

While the simulation illustrated in FIG. 13 uses a Silicon gap fillerwith a uniform dielectric constant of 2.5-3.5, in another embodiment adeformable gap filler may be fabricated that has a higher dielectricconstant in a central region to better match the dielectric constant ofthe core material, while having a lower dielectric constant in an outerregion to match the cladding of the DWGs.

FIG. 15 illustrates two DWGs 1501, 1502 coupled with a snap connecterwith a Silicon gap filler material 1512. One piece 1510 of the snapconnector is mounted on an end of DWG 1510. Another piece 1511 of thesnap connector is mounted on an end of DWG 1511. The mounting positionsof the snap connector pieces are controlled so that when mated, thedeformable gap filler material 1512 is compressed so as to eliminatemost, if not all, air from the gap between DWG 1501 and DWG 1502.

While a particular configuration of a connecter is illustrated in FIG.15, other embodiments may use any number of now known or later designedconnector designs to couple together two DWGs while maintainingmechanical alignment and providing enough coupling force to maintain adeforming pressure on the gap filler material.

Typically, the deformable material may be affixed to either the male endof DWG 1501 or to the female end of DWG 1502, for example. Thedeformable material may be affixed in a permanent manner using glue,heat fusion, or other bonding technology. However, a thinner layer ofdeformable material may be affixed to the end of both DWG 1501 and tothe end of DWG 1502 such that the gap is filled with two layers ofdeformable material.

Referring back to FIG. 8A, a DWG with a right angle corner may be usedto connect to the bottom side of an IC module, for example. Another usemay be to connect from a backplane to a PWB that is inserted into thebackplane in a perpendicular manner. As can be seen, there are many usesfor a DWG with a right angle corner. A problem is that anelectromagnetic signal travelling inside a dielectric waveguide maysuffer significant losses when traversing an abrupt corner. This is avery serious problem because dielectric waveguides applications oftenrequire them to be able to bend in a 90 degree corner and may need to doso with a short radius of curvature.

FIGS. 16A and 16B illustrate a simulation of radiated energy from aright angle corner of DWG 1601. This simulation example illustrates lossof signal in a dielectric waveguide of cross section 1×2 mm in a 90degree corner with a radius of curvature of 2 mm. As indicated at 1610of FIG. 16A, and 1612 of FIG. 16B, there is a significant amount ofenergy that is radiated out from the DWG at the outside radius of theDWG.

FIG. 17 is an illustration of a DWG 1701 that has a right angle cornerthat is shielded 1702 to minimize radiation leakage. DWG 1701 is anexample of a dielectric waveguide with metallic plating in the outerradius wall of an abrupt corner to reduce/eliminate the electromagneticwave that would escape the dielectric waveguide if the plated reflectoris not present. In general, dielectric waveguide 1701 may bemanufactured with plastic such as polypropylene, polyethylene, PMMA(Poly (methyl methacrylate), commonly referred to as Plexiglass), etc.PMMA may have a high dielectric constant value, especially when treatedwith ceramic fillers, for example, and can be used to form the coremember of a DWG. Polypropylene and polyethylene have lower dielectricconstants and may be used for cladding on the DWG. The metallic plating1702 may be done with various metallic components, such as: copper,aluminum, gold, silver, etc.

The metallic shield 1702 may be applied to the outside of the claddingon the outside radius of the corner. In another embodiment, a metallicshield may be positioned between the core member and the cladding on anoutside radius of the corner of the core member. The metallic shield maybe formed by various methods, such as: a selective plating process, byaffixing a metallic adhesive tape, by affixing a preformed metallic partusing glue or other bonding techniques, etc.

Surfaces 1704 may represent a circuit board and surface 1706 mayrepresent another circuit board that is coupled to circuit board 1704,for example. Circuit board 1704 may have various integrated circuits andother components mounted on it. For example, an IC package similar to210, 240 of FIG. 2A may be mounted on it and coupled to DWG 1701. Inanother configuration, an electronic device such as 900, 940 may bemounted on circuit board 1706 and coupled to DWG 1701. Similarly,circuit board 1706 may have electronic devices mounted on it that arecoupled to DWG 1701. In another configuration, circuit board 1706 may bea backplane that transfers a signal from DWG 1701 to another circuitboard, for example.

In another example, right angle DWG 820 of FIG. 8A may be configuredwith a corner reflector as described herein. Thus, many combinations ofcircuit boards, substrates, and electronic devices may be configured tomake use of a right angle DWG such as DWG 1701.

FIGS. 18A-18B illustrate a simulation of radiated energy from a shieldedright angle corner of a DWG. This simulation example illustrates loss ofsignal in a dielectric waveguide of cross section 1×2 mm in a 90 degreecorner with a radius of curvature of 2.5 mm. Notice the lack of radiatedenergy on the outer radius of the corner due to the presence of shield1702.

FIG. 19 is a plot illustrating insertion loss vs. frequency for a DWGwith a right angle bend between the ends of the system simulated. Plotline 1902 illustrates the insertion loss for the DWG segment with areflector on an outer radius of the corner, while plot line 1904illustrates the insertion loss for the DWG segment without a reflector.

The plating may also be extended on the sides of the dielectricwaveguide, but if all four sides are plated a metallic waveguide iscreated that has a frequency cutoff determined by the size of thedielectric waveguide. Below the cutoff frequency there is no propagationof the electromagnetic field.

While a corner that makes a bend of approximately 90 degrees isillustrated in this example, the same principles may be applied to bendsthat are larger or smaller than 90 degrees. For example, is someinstances, a bend of 180 degrees may be needed, while in otherinstances, a bend of only 45 degrees may be needed.

In this manner, a DWG with an acute bend can be made using standard DWGmaterials and known fabrication techniques that provides a low insertionloss.

FIG. 20 is an illustration of an example flexible DWG 2000. As discussedabove, for point to point communications using modulated radio frequency(RF) techniques, dielectric waveguides provide a low-loss method fordirecting energy from a transmitter (TX) to a receiver (RX). Manyconfigurations are possible for the waveguides themselves. A solid DWGwas described above with respect to FIG. 2A, for example. Generally, asolid DWG is useful for short interconnects or longer interconnects in astationary system. However, their rigidity may limit their use where theinterconnected components may need to be moved relative to each other. Aflexible waveguide configuration may have a core member made fromflexible dielectric material with a high dielectric constant (∈k1) andbe surrounded with a cladding made from flexible dielectric materialwith a low dielectric constant, (∈k2). While theoretically, air could beused in place of the cladding, since air has a dielectric constant ofapproximately 1.0, any contact by humans, or other objects may introduceserious impedance mismatch effects that may result in signal loss orcorruption. Therefore, typically free air does not provide a suitablecladding.

FIG. 20 illustrates a flexible DWG 2000 that is configured as a thinribbon of the core material surrounding by the cladding material. Inthis example, a thin rectangular ribbon of the core material 2010 issurrounded by the cladding material 2012. For sub-terahertz signals,such as in the range of 130-150 gigahertz, a core dimension ofapproximately 0.5 mm×1.0 mm works well. DWG 2000 may be manufacturedusing known extrusion techniques, for example.

FIGS. 21A-21D illustrate various configurations of a multichannelflexible DWG. There are many cases where a single DWG channel is notsufficient. For example, bi-directional communication may require twoDWG channels. A simple dual channel DWG 2100 configuration isillustrated in FIG. 21A. In this example, two core members 2101, 2102that have a higher ∈k1 value are surrounded by cladding 2108 that has alower ∈k2 value. This ribbon cable like configuration may be easilyexpanded to provide any number of multiple channels.

However, such a configuration is not always desired. As the number ofDWG “channels” increases, the width of the ribbon tends to increasewhich may not be desirable for some applications. In addition, thewaveguides themselves in a ribbon configuration are configured in anarrangement where crosstalk between adjacent waveguide channels may beintrusive, since all waveguides are essentially in the same plane. Inorder to alleviate the potential crosstalk problem, the channel spacingmay be increased or shielding may need to be added.

Another way to overcome crosstalk will now be described. This solutionprovides a convenient geometrical solution to the problem of how tobuild multiple waveguides in a cable assembly. While the implementationsillustrated here are intended for flexible cable applications, thesegeometrical solutions may also be used in rigid waveguide assemblies.

FIG. 21B illustrates a ribbon style cable 2110 in which multiplechannels are arranged as close as possible to reduce the physical sizeof the cable in order to reduce manufacturing costs and increase theinterconnect density. In this example, the adjacent DWG core members,such as 2111, 2112, are arranged in an alternating horizontal andvertical pattern of high ∈k1 ribbons surrounded by the cladding material2118. While four channels are illustrated here, two, three, or more thanfour channels may be implemented in the same ribbon by positioning themultiple channels orthogonally to each other as illustrated in FIG. 21B.This “polarized” ribbon configuration provides maximum isolation betweenthe adjacent channels without requiring an increase in the channelspacing or addition of any shielding between the channels.

FIG. 21C illustrates a stacked multiple channel DWG cable 2120. In thisexample, two rows of core members are stacked, as indicated at 2121-2123and surrounded by cladding 2128. All of the core members are positionedorthogonally to each other to minimize crosstalk. In this example, thecladding has a generally rectangular cross sectional shape.

FIG. 21D illustrates a multiple channel DWG cable 2130 in which thecladding 2138 has a generally circular cross sectional shape. In thiscase, a round cable assembly is used and the ribbons of high ∈k1material are completely surrounded by a cladding of low ∈k1 material.Note that the multiple core member ribbons, such as 2131, are positionedorthogonally to each other to reduce cross talk.

In the examples described above, the waveguides themselves areconfigured orthogonally to one another and arranged such that thespacing between the high ∈k1 “channels” is maximized. This configurationminimizes crosstalk between the channels since the RF energy on eachwaveguide is polarized. RF energy with 90 degree polarization does notinterfere with another channel. Therefore, by rotating the channels at a90 degree arrangement to each other, the spacing between channels of thesame polarity is maximized. Channels that have the opposite polarizationmode may be spaced tighter since their interference is minimized.

FIG. 21D also illustrates a flattened area 2139 that may serve as a key.In any of the implementations described above, the cable may be “keyed”in order to provide positive alignment. In the case of the rectangularribbons, a key may be added by flattening a corner, for example. Othercommon keying techniques can be applied, such as a notched cable, addingribbing to the exterior cladding, etc.

While the multiple dielectric cores are illustrated as beingapproximately the same size, in some embodiments there may bedifferences in the size of one or more cores in order to optimizetransmission efficiency for RF signals that have significantly differentwavelengths. As frequency increases, wave length decreases and thephysical size of the dielectric core may also be reduced for higherfrequency signals.

The flexible cables described above may be fabricated using standardmanufacturing materials and fabrication techniques. These cablegeometries may be built using drawing, extrusion, or fusing processes,which are all common-place to the manufacture of plastics.

However, there are many cases where a flexible DWG alone is notsufficient for an interface between two components. For example, the DWGby nature is an insulator. While it can efficiently guide high frequencyRF signals, delivering appreciable levels of power is not possible. Itmay be desirable in many cases to provide both a DC or low frequencytraditional conductive wire solution in combination with a highfrequency communication path afforded by one or more flexible DWGs.

In another example, it may be desirable to include a DWG within anexisting type of cabling system. For example, USB is a commonplaceinterconnect that provides data at 12 MBps (USB1.1), 480 Mbps (USB2.0)and 5.0 Gbps (USB3.0) using high speed conductive cabling and inaddition provides power from a host device to a peripheral device.Inclusion of a DWG in a USB would allow the same cable to be used forMBps (megabit per second) and for sub-terahertz data communication.Another example is the common power cord connecting a PC (laptop, pad,tablet, phone, etc) to a power source. This can either be the AC linesin the case of a PC or to a DC power supply. Inclusion of a DWG with thepower cable may allow using the power cable to supply power and also toprovide high speed data transfer to a network connection that isincluded with the power system of a building, for example.

An aspect these examples all have in common is that an existing cable orotherwise required cable is always covered by a dielectric material toinsulate and shield the inner metallic conductors. A combined cablesystem may exploit the outer insulator as a portion of the claddingmaterial for the DWG. By selecting an appropriate low ∈k2 material, thisinsulator will provide both the needed shielding for the inner cablingas well as the proper dielectric constant needed for confining the RFenergy in the high dielectric constant core material.

FIGS. 22-25 illustrate various ways of combining a flexible DWG with aflexible metallic cable. FIG. 22 illustrates a communication cable 2200with one or more conductive wires 2202 surrounded by a dielectric sheath2204. The sheath member has a low dielectric constant value, such as inthe range of 2.5-4.5, for example. A dielectric core member 2206 isplaced longitudinally adjacent to and in contact with an outer surfaceof sheath member 2204. The core member has a higher dielectric constantvalue that is higher than the first dielectric constant value, such asin the range of 3-12, for example. In this example, the dielectric coremember may have a rectangular cross section, approximately 0.5 mm×1.0 mmthat is suitable for sub-terahertz waves, such as approx 80-200 GHz.

A cladding 2208 surrounds sheath member 2204 and dielectric core member2206. The cladding has a dielectric constant WO value that is lower thanthe core dielectric constant value, and may be similar in value to thesheath dielectric constant. In this manner, a dielectric wave guide isformed by the dielectric core member. There may be a region indicated at2210 that includes air, or this region may be filled by deformation ofthe cladding or by other filler material that has a low dielectricconstant.

FIG. 23 illustrates a communication cable 2300 with one or moreconductive wires 2302 surrounded by a dielectric sheath 2304. In thisexample, a single layer of insulation on a metallic cable is replacedwith an outer “sandwich” of three layers. The sheath member has a low∈k2 value, such as in the range of 2.5-4.5, for example. A dielectriccore member 2306 is placed longitudinally adjacent to and in contactwith an outer surface of sheath member 2304. The core member has ahigher ∈k1 value that is higher than the first dielectric constantvalue, such as in the range of 3-12, for example. In this example, thedielectric core member 2306 completely surrounds the dielectric sheath2304. A thickness of approximately 0.5 mm thick that is suitable forsub-terahertz waves, such as approx 80-200 GHz. A third layer ofcladding 2308 surrounds sheath member 2204 and dielectric core member2306. The cladding has a lower ∈k3 value that is lower than the coredielectric constant value, and may be similar in value to the sheathdielectric constant. In this manner, a dielectric wave guide is formedby the dielectric core member. This technique may be expanded to includeadditional alternating layers of the ∈k2 and ∈k1 materials in order toprovide additional waveguides.

FIG. 24 illustrates another flexible communication cable 2400. In thisexample, many dielectric waveguides may be embedded in the insulatorssurrounding conductor cable(s) 2402. Multiple dielectric core members2406 that have a higher ∈k1 value are placed adjacent to and in contactwith an outer surface of the sheath member 2404 that has a low ∈k2value. The plurality of dielectric core members are spaced apart fromeach other and each have a cross section shape that is approximatelyrectangular. Fillers 2407 that have a lower ∈k3 value may placed betweenthe core members. An outer cladding 2408 that has a low ∈k4 value isthen placed around the multiple core members. ∈k2, ∈k3, and ∈k4 may havesimilar values in the range of 2.5-4.5, for example. In this manner,multiple dielectric wave guides may be formed.

FIG. 25 illustrates a keyed cable 2500. In any of the solutions proposedabove, the cable can be “keyed” in order to provide positive alignment.In this example, one side of the cable has a flattened profile 2520.Other common keying techniques can be applied, such as a notched cable,adding ribbing to the exterior cladding, etc.

The conductor cable, such as 2202, 2302, and 2402 may be a metallicwires, for example, or it may be another type of cable for conductingdata or energy, such as: one or more fiber optic cable, one or moretwisted pairs, such as for CATS wiring, co-axial cable, etc.

The flexible DWGs in the cables described above may be fabricated usingstandard manufacturing materials and fabrication techniques. These cablegeometries may be built using drawing, extrusion, or fusing processes,which are all common-place to the manufacture of plastics.

FIG. 26 illustrates a microelectronic package 2610 with a dipole antenna2612 coupled to a DWG 2620 that has director elements 2622 to improvecoupling of a radiated signal launched by dipole antenna 2612. Anelectro-magnetic RF wave (a modulated radio-frequency carrier signal) isgenerated by electronic circuitry contained within IC 2640 that ismounted on a substrate 2610. The RF signal is coupled into waveguide2620 that is mechanically aligned to substrate 2610. Substrate 2610 andDWG segment 2620 may both be mounted on a PCB 2600 to hold them inalignment, for example.

As described above, a dipole antenna is a good vehicle for launchingradiated energy into a dielectric waveguide. Reflector elements, such asdescribed in more detail with regard to FIGS. 2A, 5, 6, and 8A may beused to reflect wayward energy back towards DWG 2620.

In order to further improve coupling of the radiated energy into DWG2620, one or more director elements may be included within DWG 2620. Adipole has a toroidal radiation pattern symmetrical to the axis of thedipole. In order to increase the directivity and hence, decrease theinsertion losses, reflector and director(s) elements may be added. Thedipole and the reflector may reside on the same substrate 2610 as thecircuitry 2640 generating the electro-magnetic wave, as described inmore detail in FIGS. 2A, 5, 6, and 8A for example. The dipole and thefeed-lines may be implemented in a metal layer of a multi-layeredsubstrate, for example.

The reflector may be implemented as a staggered via-array in thesubstrate, as described in more detail with reference to FIGS. 5, 6, forexample. Alternatively, the reflector may be implemented as a strip ofmetal oriented parallel to the dipole antenna, for example. Thereflector strip may be grounded or it may be electrically floating.Typically, the reflector strip may be implemented on the same metallayer in which the dipole antenna is implemented. Spacing the metalreflector structure approximately one half of a wavelength from thedipole antenna provides an optimum amount of reflection. Alternatively,the reflector structure may be placed a distance of 1.5, 2.5, etcwavelengths from the dipole antenna. While a distance of one halfwavelength is optimum, a distance in the range of 0.3-0.7 or multiplesthereof provides a useful amount of reflection. Since skin effectpredominates at sub-terahertz frequencies, the thickness of the metalreflector element is not critical.

The director elements are similar in operation to a Yagi-Uda arraycommonly used in beam antennas for communication radio bands and amateurradio bands, for example. Yagi-Uda antennas are directional along theaxis perpendicular to the dipole in the plane of the elements, from thereflector toward the driven element and the director(s). Typical spacingbetween elements may vary from about 1/10 to ¼ of a wavelength,depending on the specific design. The lengths of the directors aretypically smaller than that of the driven element, which is smaller thanthat of the reflector(s) according to known antenna design principles.These elements are usually parallel in one plane.

The bandwidth of a Yagi-Uda antenna refers to the frequency range overwhich its directional gain and impedance match are preserved to within astated criterion. The Yagi-Uda array in its basic form is verynarrowband, with its performance dropping at frequencies just a fewpercent above or below its design frequency. However, by using largerdiameter conductors, among other techniques, the bandwidth may besubstantially extended.

Since the directors are passive elements, they may therefore be embeddedon the dielectric waveguide itself. Length and spacing of the elements2622 is selected to optimize directivity and bandwidth of the structurefor a given wavelength of the electromagnetic signal that is beinglaunched or received, referred to as the RF carrier frequency. Theproper spacing between the dipole and the director is maintained by themechanical alignment provided by PCB 2600, for example.

The spacing and the length of the director elements are dependent on thewavelength and the total amount of director elements used. Generally, asmore elements are used, the gain and directivity increase but thebandwidth is lowered. The design usually starts with approximate numbersusing known antenna design techniques from a textbook or guidelines. Forexample, “Antenna Theory Analysis and Design,” 1997, pages 513-532 whichis incorporated by reference herein.

Numerical modeling using known simulation tools may be used to optimizethe performance until requirements for a particular application aresatisfied. Typically, director spacing at 0.2-0.3 times wavelength workswell. A length for each director element in the range of 0.5-0.3 timeswavelength works well. Typically, director array 2612 may include twelveor fewer elements.

Table 1 lists spacing and number of elements for an example array ofdirectors 2622. Due to the high carrier frequency (>100 GHz) thedimensions of the elements given in Table 1 are rather small. However,those dimensions are based on the first resonance (close to lambda/2)and the antenna may also be designed making use of higher orderresonances, such as: lambda, 3/2lambda, etc, for example, which allowmore relaxed manufacturing tolerances.

TABLE 1 example director element length and spacing Length of Yagi-UdaArray (in wavelength) 0.4 0.8 1.2 2.2 3.2 Length of reflector 0.4820.482 0.482 0.482 0.482 Length of L3 0.442 0.428 0.428 0.432 0.428director L4 0.424 0.420 0.415 0.420 elements L5 0.428 0.420 0.407 0.407L6 0.428 0.398 0.398 L7 0.390 0.394 L8 0.390 0.390 L9 0.390 0.386 L100.390 0.386 L11 0.398 0.386 L12 0.407 0.386 (Source: “Antenna TheoryAnalysis and Design,” 1997. table 10.6)

Director elements 2612 may be molded from a metallic compound, or beplated plastic elements, for example. The set of director elements maybe connected by a center beam for support and spacing and then beembedded in an end of DWG segment 2620. Typically, fewer than twelvedirector elements would be embedded in an end of a DWG. Since skineffect is predominate at sub-terahertz frequencies, the thickness of themetal in the director elements is not critical.

In this manner, the launching structure is split into an active“feeding” section 2612, 2614 residing on the chip's package and apassive “resonating” section 2622 residing on the waveguide 2620. Thesize of the launch structure is reduced since part of it is embedded inthe dielectric waveguide itself.

FIGS. 27A-27C are multiple views of a structure for launching a sub-THzsignal from a stripline 2750 to a DWG 2720. As discussed above,launching a sub-THz electromagnetic signal from a microelectronic deviceto a dielectric waveguide is somewhat complex. On the other end of thedielectric waveguide the signal transported by the DWG needs to becaptured from the waveguide into the microelectronic device. The use ofan antenna to radiate a signal from the microelectronic device to thedielectric waveguide was described above with reference to FIGS. 2A, 5,6, and 8A-10, for example. However, an antenna needs to be verydirectional and even for the best design a significant portion of theelectromagnetic signal may be radiated in a direction different from theposition of the DWG and therefore lost in free space. Another optionwill now be described; in this example, the electromagnetic signal isconfined in its entire length from the silicon chip to the DWG.

FIG. 27A is an isometric view of a portion of a microelectronic devicethat is mounted on a substrate 2710. A transmitter or receiver in an IC(not shown) that is mounted on substrate 2710 is connected to microstrip2750. A coupling mechanism allows the micro-strip to transition into ametallic waveguide 2756 in order to couple the IC of the microelectronicdevice with the dielectric waveguide 2720.

The microstrip line 2750 coming from the silicon chip has an impedancematched to the silicon die of the IC. Typically this impedance is 50ohms. The impedance of microstrip 2750 is determined by itscross-section shape and the distance between it and ground plane 2752,as is well known. Ground plane 2752 extends under the length ofmicrostrip 2750 and the distance between microstrip 2750 and groundplane 2752 is controlled to be uniform.

FIG. 27B is a side view illustrating in more detail how metallicwaveguide 2758 is used to transition from the micro-strip line to theDWG. Ground plane 2752 is connected to the top side of the metallicwaveguide 2756 as indicated at 2753 and the micro-strip trace 2750 isconnected to the bottom side of the metallic waveguide as indicated at2751. As described above, dielectric waveguide 2720 has a core membermade from dielectric material with a high dielectric constant (∈k1) andis surrounded with a cladding made from dielectric material with a lowdielectric constant, (∈k2). The segment of DWG 2720 may be flexible orrigid material, as described above. Core member 2725 may be made fromvarious types of dielectric materials, as described in more detailabove. A polymer plastic is a typical material used for core member2725. An extension 2727 of the dielectric core member 2725 extendsinside the metallic waveguide 2756. The dielectric core member extension2727 extends past the cladding 2726 for a first distance, and thentapers down to an edge over a second distance, such that the interior ofmetallic waveguide 2756 is essentially completely filled by dielectriccore extension 2727.

Typically, metallic waveguide 2756 is mounted to package substrate 2710during assembly using a solder reflow process, for example. The polymerplastic DWG typically could not survive the temperature of the reflowprocess, so extension 2727 of DWG 2720 will be inserted into themetallic waveguide 2756 after the reflow process.

Notice how the thickness of the extension portion 2726 of the coremember increases in a linear manner in the transition area from point2753 to point 2751. In this region, the width of the microstrip istapered to form a tapered microstrip segment 2754 that is illustrated inmore detail in FIG. 27C. It is beneficial to linearly increase the widthof the microstrip trace in order to match the impedance of themicrostrip line with the impedance of the metallic waveguide 2756.Simulations have determined that an optimum taper is one thattransitions from the width corresponding to 50 ohm line 2750 to thewidth of the metallic waveguide at the other end 2751 of the transitionarea.

Substrate 2710 may be mounted onto a larger substrate, such as PCB 2700,for example, by solder bumps, not shown, using a solder reflow process,for example. Dielectric waveguide 2720 may then be mounted onto PCBsubstrate 2700 using a mounting scheme, such as: an adhesive, amechanical retention device, etc. Extension 2727 of the dielectric coremember 2725 extends inside the metallic waveguide 2756 and fills theinside region of the metallic waveguide. In this manner, a highlyefficient transfer function is produced between the microstrip line andthe DWG.

FIG. 28 illustrates simulation results for various length metallicwaveguide transitions. These S-parameter plots were obtained from anHFSS simulation of the coupler design above. In this example, the familyof curves corresponds to different lengths of the metallic waveguides.S-parameters refer to the scattering matrix (“S” in S-parameters refersto scattering). S-parameters describe the response of an N-port networkto voltage signals at each port. The scattering matrix is a mathematicalconstruct that quantifies how RF energy propagates through a multi-portnetwork. The S-matrix is what allows the properties of a complicatednetwork to be described as a simple “black box”. For an RF signalincident on one port, some fraction of the signal bounces back out ofthat port, some of it scatters and exits other ports (and is perhapseven amplified), and some of it disappears as heat or evenelectromagnetic radiation. The first number in the subscript refers tothe responding port, while the second number refers to the incidentport. Thus S21 means the response at port 2 due to a signal at port 1.The three sets of parameters plotted in FIG. 28 represent the S11, S12and S22 parameters for metallic waveguides that have a length of 0.8 mm,0.85 mm, 1.0 mm, and 1.2 mm for frequencies from 100-180 GHz.

FIG. 29 is an isographic view of a horn antenna used to launch a signalfrom a microstrip line to a DWG. As discussed above, launching andreceiving a sub-THz electromagnetic signal from a microelectronic deviceto a dielectric waveguide (DWG) requires a well designed couplingscheme. While several techniques have been described above, a problemwith using antennas to launch a signal into a dielectric waveguide isthat, if not properly designed, a big portion of the electromagneticsignal may be lost due to radiation in directions different from wherethe dielectric waveguide is located.

A coupling apparatus that uses multiple copper layers within thesubstrate of a microelectronic package to build a horn antenna tointerface with a dielectric waveguide will now be described. Thisapparatus is able to emit a very directional beam that is aligned withthe dielectric waveguide and thereby provide an efficient energytransfer. This interface may be used to launch an electromagnetic signalfrom a silicon chip mounted in the same package substrate to thedielectric waveguide. The same type interface may be used at the otherend of the dielectric waveguide to read the electromagnetic signal sentby the transmitter.

Referring still to FIG. 29 and to FIGS. 30A-30B, package substrate 2910is a multilayer substrate that has multiple conductive layers 2911,typically copper, separated by layers of insulation, such as: printedcircuit board material, ceramic material, etc, for example. As is wellknown, conductive layers in a multilayer substrate may be patternedduring fabrication of the multilayer substrate to form variousconductive shapes and interconnect wire patterns.

Horn antenna 2960 has a generally trapezoidal, or horn shaped top plate2961 and bottom plate 2962 formed in different layers of the multilayersubstrate 2910 with a set of densely spaced vias 2962 forming twosidewalls of the horn antenna by coupling adjacent edges of the topplate and the bottom plate. The horn antenna has a narrow input end 2972and a wider flare end 2970. A portion 2973 of the input end may beconfigured as a rectangular metallic waveguide. Metallic waveguide 2973provides an interface between microstrip line 2950 and horn antenna2960. In other implementations, a horn antenna may interface to themicrostrip line using a different type of feed mechanism. However, arectangular metallic waveguide is convenient and easy to implement inthe multilayer substrate.

A microstrip line 2950 is coupled to the top plate and a ground planeelement 2952 is coupled to the bottom plate at the input end of thewaveguide. Microstrip line 2950 is positioned above ground plane element2952 and has a geometric cross section that is designed to produce anapproximately uniform transmission line impedance, typicallyapproximately 50 ohms. Of course, the cross section shape and the amountof separation between the microstrip line and the ground plane elementmay be varied to produce a different impedance to match a particulartransmitter amplifier or receiver low noise amplifier.

To form the horn antenna and the rectangular waveguide, a tight array ofstaggered vias 2962 forms the vertical sidewalls of the horn antenna andwaveguide. In addition, a set of filament lines 2963 may be formed inthe multilayer substrate in each intermediate copper layer between thetop and the bottom layer and used to join the vias at each copper levelto improve the reflective characteristic of the via walls. The number offilaments is determined by the number of conductive layers in themultilayer substrate 2910. In this example there or five layersavailable for filament lines 2963. Other embodiments may have fewer ormore. More filaments are preferred from a performance view in order toapproximate a solid wall as much as the substrate manufacturing ruleswould allow. However, the number depends on the availability of varioussubstrate layer thicknesses. Typically the goal is to minimize cost, sofewer layers, just enough to provide the required performance andfunction, may be a design goal. Each filament may be just wide enough tointerconnect the staggered row of vias on a given side, or they may beas wide as the staggered row of vias, for example. In anotherembodiment, one or more filament lines may be part of a larger groundplane that extends beyond the horn antenna and waveguide, however, thefilament lines should not intrude into the interior portion of the hornantenna and waveguide.

Microstrip line 2950 may have a tapered section 2951 that increases inwidth as it approaches the horn antenna. Tapered section 2951 providesimpedance matching to match the impedance of the microstrip line to thatof the substrate-integrated rectangular waveguide that feeds thesubstrate-integrated sectoral horn antenna. The taper provides animpedance match over a broad frequency band.

The microstrip line may be on the same conductive layer as the top ofthe horn, as illustrated in this example; however, it does not have to.It may be on an inner layer that is then connected to the top of thehorn by a via where the microstrip flare connects to the rectangularwaveguide. When the microstrip line is on an inner layer, it should notrun through the inside of the rectangular waveguide and the horn sincethat would change the wave propagation properties of the wholerectangular-waveguide/horn antenna structure. The intent is to smoothlytransition from the microstrip line medium of wave propagation, theninto the rectangular waveguide medium of wave propagation, andultimately radiate the field out of the horn antenna.

The ground strip element is coupled to the bottom plate 2962 to minimizewave propagation discontinuity between the microstrip line and therectangular waveguide/horn antenna structure.

The horn antenna lateral dimensions (the flare angle, the horn length,the flare width) are chosen to provide an end-fire radiation with verylow back lobes and with an optimized gain. In free-space the longer thehorn the higher the gain, but in a lossy substrate the long horn suffersfrom high substrate. Therefore, in order to minimize loss, horn lengthand exact dimensions are selected to achieve a higher gain withoutminimal loses based on the frequency of operation and the material usedto fabricate the multilayer substrate. Typically, the interior materialof the horn may be PCB/PWB substrate or IC package substrate material.An initial set of dimensions may be selected based on known antennaanalysis techniques. Simulation, as described above, may then be used torefine the dimensions for a particular operating frequency and substratematerials, for example.

The horn antenna height is chosen to support the required rectangularwaveguide cut-off frequency for the dominant mode, which in this case isTE10. The height of the horn is also constrained by the thickness ofmultilayer substrate 2910. However the distance between the top and thebottom is, in this example, limited by the distance between the top Culayer and the bottom Cu layer. The dimensions of the waveguide determinethe cutoff frequency, therefore, a design constraint is that thedistance between the top and bottom plates provide a cutoff frequencyabove an expected frequency of operation.

Substrate 2910 may be mounted onto a larger substrate, such as PCB 2900,for example, by solder bumps, not shown, using a solder reflow process,for example. Dielectric waveguide 2720 may then be mounted onto PCBsubstrate 2700 using a mounting scheme, such as: an adhesive, amechanical retention device, etc. In this manner, a highly efficienttransfer function is produced between the microstrip line and the DWG.

FIG. 31 illustrates a simulation of signal radiation from the hornantenna of FIG. 29. This electromagnetic simulation was performed usingthe Ansys HFSS simulator. As can be seen in the illustration, a signalthat is launched from the micro-strip line 2950 is launched into coremember 2925 or DWG 2920 with minimal radiation loss. The beam out ofhorn antenna 2960 is very narrow with high directivity that is easy tofocus into the DWG core.

FIG. 32 illustrates use of an RJ45 connector 3280 for coupling a DWG3220 to a compatible receptacle. Based on the descriptions above ofvarious ways to interface segments of DWG, some sort of mechanicalcoupling is generally required to maintain the ends of two DWG segmentsin proper alignment. The connection should be easy to establish,reliable, and pluggable. The connector must satisfy the tolerances formechanical alignment of the waveguides. One example mechanical connectorwas illustrated in FIG. 15. Another option will now be described.

The RJ45 connector is widely used for Ethernet networking applications.In its well known form, it may have up to four wire pairs (8 wirestotal) for electrical data transmission. Example RJ45 connector 3280incorporates one or more waveguides into a standardized RJ45 connectorbody.

In order to maintain the same footprint as a standard RJ45 connector,some or all of the electrical contacts are removed to provide room fordielectric waveguides. Since the dielectric waveguide is inherentlyisolating, a few electrical contacts 3284 may be retained for providingpower for external periphery, for example. The electrical contacts maybe coupled to wires that are included with DWG 3220 as described abovein more detail with regard to FIGS. 22-24, for example. Similarly, oneor more DWG cores illustrated in cable 2110 of FIG. 21 may be replacedwith a copper or other conductive wire or twisted pair of wires. Theelectrical connectors may be coupled to the wires using the known crimptechnology used in standard RJ45 connectors.

RJ45 coupler 3280 has a dielectric connector housing 3281. It may have alocking tab 3282 to interlock with a matching receptacle. DWG 3220 mayhave a single core, or multiple cores, as described in more detailabove. DWG 3220 will typically be flexible, but it may also be rigid, asdescribed with respect to FIG. 2B, 3, for example.

A flexible waveguide configuration may have a core member 3225 made fromflexible dielectric material with a high dielectric constant (∈k1) andbe surrounded with a cladding 3226 made from flexible dielectricmaterial with a low dielectric constant, (∈k2). While theoretically, aircould be used in place of the cladding, since air has a dielectricconstant of approximately 1.0, any contact by humans, or other objectsmay introduce serious impedance mismatch effects that may result insignal loss or corruption. Therefore, typically free air does notprovide a suitable cladding.

The ends of core members 3225 may be flat, or they may have a spearshape or conical shape, as described above in more detail with respectto FIG. 12, for example. A deformable gap filling material may also beincluded in the end of DWG 3220, as described in more detail withrespect to FIG. 13, for example.

Connector housing 3281 may be attached to DWG 3220 using an adhesive orother bonding material, for example. When electrical contacts arecrimped to wires that are included with DWG 3220, then that alone may besufficient to retain DWG 3220 within connector housing 3281.

In this manner, a low cost, easy to implement, mechanicallyself-aligning coupling scheme is provided.

FIGS. 33-34 illustrates various applications of an RJ45 connector forcoupling a DWG. FIG. 33 illustrates an electronic system that mayinclude a PCB or other base substrate 3300. An integrated circuit 3340that include sub-THz transmission or receiver circuitry may be mountedon a carrier substrate 3310 and coupled to a DWG segment 3320 using anyof the techniques described above in more detail. A female RJ45connector 3385 may also be mounted on base carrier 3320 and coupled toDWG 3320, in a similar manner as described with regard to FIG. 32. Theends of the core members in DWG 3320 may be flat, or they may have aspear shape or conical shape, as described above in more detail withrespect to FIG. 12, for example. A deformable gap filling material mayalso be included in the end of DWG 3220, as described in more detailwith respect to FIG. 13, for example. Female RJ45 connector may alsoinclude electrical contacts for mating with electrical contacts 3284,for example. Male RJ45 connector 3280 may then be easily inserted intoconnector 3385 for a positive mechanical and signal connection.

Similarly, a female RJ45 connector 3485 may be affixed to a flexible orrigid DWG segment 3420. The ends of the core members in DWG 3420 may beflat, or they may have a spear shape or conical shape, as describedabove in more detail with respect to FIG. 12, for example. A deformablegap filling material may also be included in the end of DWG 3420, asdescribed in more detail with respect to FIG. 13, for example. In thismanner, two flexible or rigid DWGs may be easily and quickly mated.

FIG. 35 is a flow chart illustrating use of a dielectric waveguide in asystem. A system integrator or a system user may connect 3502 a firstelectronic system to a second electronic system using a DWG. The twosystems may be simply two different ICs that may be part of largersystem, for example, that is being assembled by a system integrator. Thetwo systems may be a computing device and a peripheral device or twocomputing devices that a user is connecting together for personal orbusiness use, for example. The systems may be any form of computingdevice, such as, but not limited to: a rack mount, desk mount, orportable computer, a mobile user device such a notebook computer, atablet computer, a smart phone, etc, for example. The systems may be anytype of peripheral device such as: a media storage device such asrotating or solid state disk drive, a modem or other interface to a highspeed network, etc, for example.

The DWG may be any form of flexible of rigid DWG as described in moredetail above, for example. The DWG may be a combination cable asdescribed above, such as an enhanced USB cable that includes a DWG, forexample. The connection may use an RJ45 connector, as described in moredetail above. There may be a single DWG, or there may be multiple DWGs,depending on the requirements of the systems.

Once the system are connected and turned on, a sub-terahertz RF signalmay be generated 3504 by an IC in the first system. A stream or multiplestreams of data may be modulated onto the RF signal using knownmodulation techniques. The RF signal is then transferred 3506 from theIC and launched 3508 into the DWG using any of the coupling techniquesdescribed in more detail herein.

The second system may then capture 3510 the radiated RF signal from theDWG and transfer 3512 the captured RF signal using any of the couplingtechniques described in more detail herein. An IC within the secondsystem may then demodulate the RF signal to recover the one or morestreams of data for use within the second system.

Two DWGs may be used for bidirectional transfer of data, or a single DWGmay be used by providing transceivers in each of the two systems.

FIG. 36 is an illustration of two systems 3601, 3602 beinginterconnected with a DWG 3620. The two systems may be a computingdevice and a peripheral device or two computing devices that a user isconnecting together for personal or business use, for example. Thesystems may be any form of computing device, such as, but not limitedto: a rack mount, desk mount, or portable computer, a mobile user devicesuch a notebook computer, a tablet computer, a smart phone, etc, forexample. The systems may be any type of peripheral device such as: amedia storage device such as rotating or solid state disk drive, a modemor other interface to a high speed network, etc, for example.

DWG 3620 may be any form of flexible of rigid DWG as described in moredetail above, for example. The DWG may be a combination cable asdescribed above, such as an enhanced USB cable that includes a DWG, forexample. The connection may use an RJ45 connector as described in moredetail above. There may be a single DWG, or there may be multiple DWGs,depending on the requirements of the systems.

Connectors 3621 and 3622 may be inserted into matching receptacles 3611,3612 by a user or system integrator. The connectors and receptacles maybe RJ45 style connectors, as described above with reference to FIGS.32-34, or any other type of connector that provides alignment for DWG3620.

Each system 3601, 3602 may contain a PWB or other type substrate onwhich are mounted one or more integrated circuits as described above inmore detail that produce or receive a sub-terahertz signal that iscoupled to a DWG that is then terminated in receptacles 3611, 3612. Themanner of coupling between the IC and the DWG may be implemented usingany of the techniques described above in more detail, for example.

As shown by the above descriptions and examples, two or more electronicdevices may be easily interconnected to provide sub-terahertzcommunication paths between the electronic devices by using thetechniques described herein.

Other Embodiments

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various other embodiments of the invention will beapparent to persons skilled in the art upon reference to thisdescription. For example, several of the techniques described herein maybe combined in various manners. For example, the various matinginterface configurations described with reference to FIGS. 11-15 may beapplied to the output end of any of the DWG segments described withreference to FIGS. 2A-2D, 5, 8A, 21A-21D, 22-27, 29, and 32, etc, forexample. The connectors described in FIGS. 15, 32 and 33 may be appliedto any of the DWG segments described herein. Various ones of the DWGsdescribed herein may be coupled to any of the various launchingstructures described herein. Multiple launching structures may be usedfor DWG cables that have multiple core members, as described herein.Other combinations not explicitly recited here may be made.

Certain terms are used throughout the description and the claims torefer to particular system components. As one skilled in the art willappreciate, components in digital systems may be referred to bydifferent names and/or may be combined in ways not shown herein withoutdeparting from the described functionality. This document does notintend to distinguish between components that differ in name but notfunction. In the following discussion and in the claims, the terms“including” and “comprising” are used in an open-ended fashion, and thusshould be interpreted to mean “including, but not limited to . . . . ”Also, the term “couple” and derivatives thereof are intended to mean anindirect, direct, optical, and/or wireless electrical connection. Thus,if a first device couples to a second device, that connection may bethrough a direct electrical connection, through an indirect electricalconnection via other devices and connections, through an opticalelectrical connection, and/or through a wireless electrical connection.

Although method steps may be presented and described herein in asequential fashion, one or more of the steps shown and described may beomitted, repeated, performed concurrently, and/or performed in adifferent order than the order shown in the figures and/or describedherein. Accordingly, embodiments of the invention should not beconsidered limited to the specific ordering of steps shown in thefigures and/or described herein.

It is therefore contemplated that the appended claims will cover anysuch modifications of the embodiments as fall within the true scope andspirit of the invention.

What is claimed is:
 1. A system comprising: a multilayer substrate formounting an integrated circuit; a microstrip line formed in one of thelayers of the multilayer substrate, wherein the microstrip line isformed parallel to a ground plane element that is located in another oneof the layers of the multilayer substrate; and a metallic waveguidemounted on the multilayer substrate, wherein the metallic waveguide hasan open end formed by a top, bottom and sides configured to receive acore member of a dielectric waveguide, and an opposite tapered endformed by declining the top of the metallic waveguide past the bottom ofthe metallic waveguide and down to contact the multilayer substrate,wherein a pinnacle of the tapered end is coupled to the ground planeelement, and wherein the bottom side of the metallic waveguide is incontact with the multiplayer substrate and coupled to the microstripline.
 2. The system of claim 1, wherein the microstrip line linearlyincreases in width from a point proximate where the pinnacle of thetapered end is coupled to the ground plane to a width approximatelyequal to a width of the metallic waveguide at point where the microstripline is coupled to the metallic waveguide.
 3. The system of claim 1,further comprising an integrated circuit (IC) mounted on the multilayersubstrate, wherein a radio frequency circuit within the IC is coupled tothe microstrip line.
 4. The system of claim 3, further comprising adielectric waveguide with an extended core member extending into theopen end of the metallic waveguide.
 5. The system of claim 4, furthercomprising a system substrate, wherein the multilayer substrate and thedielectric waveguide are mounted on the system substrate.
 6. The systemof claim 4, wherein an opposite mating end of the DWG is configured in anon-planer shape for mating with a second DWG having a matchingnon-planar shaped mating end.
 7. The system of claim 6, wherein thenon-planer shape is selected from a group consisting of a V shape, apyramid shape, a conical shape, and a vaulted shape.
 8. The system ofclaim 6, wherein a surface of the mating end is covered with adeformable material.
 9. The system of claim 4, further comprising acoupling mechanism attached to an opposite mating end of the DWG,wherein the coupling mechanism is configured to retain a complimentarycoupling mechanism on a mating end of a second DWG, wherein the couplingmechanism is an RJ45 compatible connector.
 10. A method of operating anelectronic device, the method comprising: generating a sub-terahertzsignal in an integrated circuit within the electronic device;transporting the sub-terahertz signal to a tapered metallic waveguidelocated on a multilayer substrate of the electronic device; andradiating a portion of the sub-terahertz signal from the taperedmetallic waveguide into a dielectric waveguide.
 11. The method of claim10, wherein the sub-terahertz signal is transported by a microstrip lineformed in one of the layers of the multilayer substrate, wherein themicrostrip line is formed parallel to a ground plane element that islocated in another one of the layers of the multilayer substrate. 12.The method of claim 11, wherein the metallic waveguide has an open endformed by a top, bottom and sides configured to receive a core member ofa dielectric waveguide, and an opposite tapered end formed by decliningthe top of the metallic waveguide past the bottom of the metallicwaveguide and down to contact the multilayer substrate, wherein apinnacle of the tapered end is coupled to the ground plane element, andwherein the bottom side of the metallic waveguide is in contact with themultiplayer substrate and coupled to the microstrip line.
 13. The methodof claim 12, wherein the microstrip line linearly increases in widthfrom a point proximate where a pinnacle of the tapered metallicwaveguide is coupled to a ground plane to a width approximately equal toa width of the metallic waveguide at point where the microstrip line iscoupled to the metallic waveguide.
 14. A dielectric waveguide (DWG)comprising: a dielectric core member, wherein the core member has afirst dielectric constant value; a cladding surrounding the dielectriccore member, wherein the cladding has a second dielectric constant valuethat is lower than the first dielectric constant; and wherein at a firstmating end of the DWG, a dielectric core extension extends past thecladding for a first distance, and then tapers down to an edge over asecond distance, such that when inserted into a tapered metallicwaveguide the interior of metallic waveguide is essentially completelyfilled by dielectric core extension.